This invention pertains to catalytic multi-stage hydrodesulfurization of metals-containing petroleum residua feedstocks. It pertains particularly to a process for deep hydrodesulfurization of such feedstocks which utilizes in the first stage catalytic reactor used particulate catalyst withdrawn from the second stage reactor and rejuvenated, so as to reduce overall fresh catalyst consumption for the process.
Some usage of regenerated catalysts in catalytic hydroconversion of hydrocarbon feedstocks is generally known. For example, U.S. Pat. No. 3,893,911 to Rovesti et al discloses a multi-stage catalytic ebullated bed demetallization process for petroleum feedstocks in which used catalyst in the first stage reactor is withdrawn and treated to remove carbon deposits without any removal of contaminant metals, then returned to the first stage reactor for reuse. However, because such treated catalyst becomes further contaminated with additional metals deposits, the process requires high catalyst replacement rates and provides undesirably low levels of hydrodesulfurization activity. U.S. Pat. No. 4,576,710 to Nongbri et al discloses a catalytic desulfurization process in which used catalyst from ebullated bed reactors is withdrawn and treated for carbon removal only, including minor transfer of second stage used but untreated catalyst to the first stage reactor. However, the process is not suitable for deep desulfurization of high metals-containing petroleum feedstocks, because without contaminant metals removal from the used catalyst, increased metals loadings on the treated catalyst results in low catalytic activity and undesirably high catalyst consumption for the process.
Some rejuvenation methods for used particulate catalysts to remove contaminant metals and carbon are also known. For example, U.S. Pat. Nos. 4,454,240 and 4,595,600 to Ganguli each describe a process for treating used catalysts withdrawn from hydroconversion reactors for hydrocarbon feedstreams so as to remove contaminant metals and carbon from the used catalyst. Also, U.S. Pat. No. 4,769,219 to Tasker et al discloses an apparatus and method for treating particulate used catalyst in a single vessel to remove heavy oils, contaminant metals, and coke deposits from the catalyst and provide a rejuvenated catalyst material suitable for further use.
However, these known processes for catalytic hydroprocessing of petroleum residua feedstocks do not adequately address the problem of high contaminant metals loading and resulting low catalytic activity in the first stage reactor for desulfurization of high metals-containing petroleum residua feeds. Thus, further process improvements are desirable, particularly for deep hydrodesulfurization of high metals-containing petroleum residua feedstocks to obtain desulfurized hydrocarbon liquid products while achieving reduced overall catalyst usage. Such process improvements can be achieved by adding rejuvenated second stage catalyst to the first stage reactor, so that the first stage reactor catalyst has reduced contaminant metals loading and has catalytic activity which is close to that of fresh catalyst.